Telomerase inhibitors

ABSTRACT

Methods and compositions for treating cancer and other diseases in which inhibition of telomerase activity can ameliorate disease symptoms or prevent or treat the disease relate to compounds that are derivatives of pyridine aldehydes, thioaldehyde, acetals, or thioacetals. Such compounds are characterized by the following structure: ##STR1## X 1  is selected from the group consisting of oxygen, sulfur, sulfone, sulfinyl, and --NR-- where R is hydrogen, alkyl, aryl, and aralkyl. R 1  is --Y n  R 6 , in which n is an integer between 0 and 10 and each Y n  for n greater than 0 independently is methylene, methine, or quarternary carbon. R 6 , for any value of n (i.e., n is zero or non-zero), is alkyl, aryl, heterocycle, heteroaryl, aralkyl, heteroaralkyl, alkylcarbonyl, arylcarbonyl, heteroarylcarbonyl, heteroaralkylcarbonyl, aralkylcarbonyl, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, and arylsulfonyl. R 6  can also be a linker L selected from the group consisting of alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl, to which linker between 1 and 3 additional compounds having the structure shown as Compound I above are attached to form thereby homogeneous or heterogeneous poly pyridine aldehydes, acetals, or thioacetals as described in greater detail below. R 2  is hydrogen, alkyl, aryl, hydroxyl, alkoxyl, aryloxyl, halogen, cyano, amino, alkylamino, arylamino, dialkylamino, diarylamino, arylalkylamino, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, or arylsulfonyl. R 3  and R 4  are selected independently from the group consisting of hydrogen, halogen, hydroxyl, aryloxyl, alkoxyl, lower alkyl, aryl, heteroaryl, aralkyl, cyano, carboxyl, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, heteroaralkyl, nitro, amino, alkylamino, arylamino, dialkylamino, diarylamino, and arylalkylamino. Finally, R 5  is selected from the group consisting of bis(alkoxy)methyl, bis(alkylthio)methyl, and --HC═X 2 , where X 2  is oxygen or sulfur.

NOTICE OF U.S. GOVERNMENT RIGHTS

A portion of the work described herein was funded in part by SBIR Grant No. 1 R43 CA65178-01. The U.S. Government may therefore have certain rights relating to this invention.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to human telomerase, a ribonucleoprotein enzyme involved in human telomere DNA synthesis, and to compounds that inhibit telomerase activity. The invention provides methods, compounds and compositions relating to the fields of molecular biology, chemistry, pharmacology, oncology and medicinal and diagnostic technology.

2. Description of Related Disclosures

The war on cancer has raged for over two decades. Yet, despite the expenditure of over a billion dollars for research and development of new technologies to diagnose and treat malignancies, the age-adjusted cancer mortality rate in the U.S. has remained largely unchanged for the past forty years. Indeed, if current epidemiological trends continue, it appears likely that cancer will overtake cardiovascular disease as the leading cause of death in the United States.

To be sure, some battles have been won and much has been learned about the enemy. A few cancers (e.g., Hodgkin's disease) are now considered curable, and treatment regimes for many other cancers have improved over the last decade. In addition, there has been an explosion of information describing the regulatory mechanisms involved with the onset of malignancy, including the roles of growth factors, receptors, signal transduction pathways, oncogenes, and tumor suppressor genes in the control of cell growth and differentiation. However, these successes are overshadowed by the fact that cancer is a highly heterogeneous disease in which profound differences exist in the mechanisms by which different cell types become malignant. Thus, although we know more about the mechanisms by which cells become malignant than ever before, each type of cancer presents a unique set of problems in terms of treatment.

Because the cellular mechanisms leading to cancer are so heterogeneous, research on such mechanisms is unlikely to yield a general approach to cancer treatment that is effective and well tolerated by cancer patients. Presently, a variety of non-specific treatment modalities are available, including surgery, radiation, and a variety of cytoreductive and hormone-based drugs, used alone or in combination. Some oncolytic drugs are also available, but the efficacy of these drugs varies among cancer types. Thus, patients suffering from cancer often are forced to undergo treatments that are highly non-specific and highly toxic. Commonly, the toxicity of the treatments produces severe side effects, including nausea and vomiting, hair loss, diarrhea, fatigue, ulcerations and the like, which severely impact the patient's quality of life. In some cases, the impact on the patient's quality of life can be so great that the patient is unable to continue the full course of therapy or opts out of treatment entirely.

Recently, however, an understanding of the mechanisms by which normal cells reach the state of senescence, ie., the loss of proliferative capacity that cells normally undergo in the cellular aging process, has begun to emerge. The DNA at the ends, or telomeres, of the chromosomes of eukaryotes usually consists of tandemly repeated simple sequences. Scientists have long known that telomeres have an important biological role in maintaining chromosome structure and function. More recently, scientists have speculated that the cumulative loss of telomeric DNA over repeated cell divisions may act as a trigger of cellular senescence and aging, and that the regulation of telomerase, an enzyme involved in the maintenance of telomere length, may have important biological implications. See Harley, 1991, Mutation Research, 256:271-282, incorporated herein by reference.

Telomerase is a ribonucleoprotein enzyme that synthesizes one strand of the telomeric DNA using as a template a sequence contained within the RNA component of the enzyme. See Blackburn, 1992, Annu. Rev. Biochem,. 61:113-129, incorporated herein by reference. Methods for detecting telomerase activity, as well as for identifying compounds that regulate or affect telomerase activity, together with methods for therapy and diagnosis of cellular senescence and immortalization by controlling telomere length and telomerase activity, have also been described. See Feng, et al., 1995, Science, 269: 1236-1241; Kim, et al., 1994, Science, 266: 2011-2014; PCT patent publication No. 93/23572, published Nov. 25, 1993; U.S. patent application Ser. Nos. 08/288,501, filed Aug. 10, 1994; 08/330,123, filed Oct. 27, 1994, now U.S. Pat. No. 5,523,016; 08/272,102, filed Jul. 7, 1994, now abandoned; 08/255,774, filed Jun. 7, 1994; 08/315,214, and 08/315,216, both of which were filed Sep. 28, 1994; 08/151,477 and 08/153,051, now U.S. Pat. No. 5,618,668, both of which were filed 12 Nov. 1993; 08/060,952, filed 13 May 1993; and 08/038,766, filed 24 Mar. 1993, now U.S. Pat. No. 5,489,503. Each of the foregoing patent applications and reference is incorporated herein by reference.

The identification of compounds that inhibit telomerase activity provides important benefits to efforts at treating human disease. Compounds that inhibit telomerase activity can be used to treat cancer, as cancer cells express telomerase activity and normal human somatic cells do not express telomerase activity at biologically relevant levels (ie., at levels sufficient to maintain telomere length over many cell divisions). Unfortunately, few such compounds have been identified and characterized. Hence, there remains a need for compounds that act as telomerase inhibitors and for compositions and methods for treating cancer and other diseases in which telomerase activity is present abnormally. The present invention meets these and other needs.

SUMMARY OF THE INVENTION

The present invention provides methods, compounds and compositions that are highly unique, specific and effective for treating malignant conditions by targeting cells having telomerase activity. The methods, compounds and compositions of the invention can be applied to a wide variety of malignant cell types and avoid the problems inherent in current cancer treatment modalities, which are non-specific and toxic.

In a first aspect, the present invention provides novel methods, compositions and compounds relating to a class of telomerase inhibiting agents that are derivatives or analogues of pyridine. These telomerase inhibiting compounds have the general structure shown below (Compound I): ##STR2## In compound I, X₁ is selected from the group consisting of oxygen, sulfur, sulfone, sulfinyl, and --NR-- where R is hydrogen, alkyl, aryl, and aralkyl. R₁ is --Y_(n) R₆, in which n is an integer between 0 and 10 and each Y_(n) for n greater than 0 independently is methylene, methine, or quarternary carbon. R₆, for any value of n (i.e., n is zero or non-zero), is alkyl, aryl, heterocycle, heteroaryl, aralkyl, heteroaralkyl, alkylcarbonyl, arylcarbonyl, heteroarylcarbonyl, heteroaralkylcarbonyl, aralkylcarbonyl, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, and arylsulfonyl. R₆ can also be a linker L selected from the group consisting of alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl, to which linker between 1 and 3 additional compounds having the structure shown as Compound I above are attached to form thereby homogeneous or heterogeneous poly pyridine aldehydes, acetals, or thioacetals as described in greater detail below. R₂ is hydrogen, alkyl, aryl, hydroxyl, alkoxyl, aryloxyl, halogen, cyano, amino, alkylamino, arylamino, dialkylamino, diarylamino, arylalkylamino, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, or arylsulfonyl. R₃ and R₄ are selected independently from the group consisting of hydrogen, halogen, hydroxyl, aryloxyl, alkoxyl, lower alkyl, aryl, heteroaryl, aralkyl, cyano, carboxyl, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, heteroaralkyl, nitro, amino, alkylamino, arylamino, dialkylamino, diarylamino, and arylalkylamino. Finally, R₅ is selected from the group consisting of bis(alkoxy)methyl, bis(alkylthio)methyl, and --HC═X₂, where X₂ is oxygen or sulfur.

In one embodiment, the present invention includes derivatives of the general structure shown above in which R₅ is aldehyde, R₂ is cyano, X₁ is sulfur, n is 1, Y is methylene or methylmethine (--CH(CH₃)--), and R₆ is aryl or heteroaryl. More specifically, useful compounds provided by the present invention include those in which R₆ is aryl. These compounds have the generic structure shown below: ##STR3## In this compound, R₇ -R₁₁ are selected independently from the group consisting of hydrogen, alkyl, aryl, aralkyl, halogen, alkoxyl, aryloxyl, aralkoxyl, heterocycle, and nitro. In addition, adjacent phenyl ring substituents together can form a 5- or 6-membered cyclic alkyl ether or carbocycle ring fused to the phenyl ring of the benzylthioether moiety of the compound. Useful compounds of this general structure include those for which R₃ and R₄ are hydrogen and R₇ -R₁₁ are selected independently from the group consisting of hydrogen, methyl, ethyl, 2-phenylethenyl, trifluoromethyl, fluoro, chloro, bromo, phenyl, benzyloxy, trifluoromethoxy, isopropyl, and nitro, as well as those compounds in which adjacent substituents together can function as points of attachment for the groups --Z₁ --CH₂ --Z₂ --Z₃ -- or --O--(CH₂)_(p) --O--, where Z₁ -Z₃ are selected independently from the group consisting of oxygen, methylene and dimethylmethylene, and p is 1 or 2.

In another aspect, the present invention includes derivatives of Compound I in which n is 1, Y is methylene, and R₆ is a linker L selected from the group consisting of aryl and alkyl. This compound has the structure shown below: ##STR4## The subscript m is an integer between 2 and 4. One particular embodiment of that in which X₁ is sulfur and R₂ is cyano. More specific embodiments include those in which R₅ aldehyde and L is phenylene or substituted phenylene as shown below: ##STR5##

Yet other useful embodiments are those for which m is 2, R₂ -R₅ are as recited above, X₁ is sulfur, R₅ is aldehyde, and L is alkyl, especially those for which L is selected from the group consisting of ethylene (--CH₂ --CH₂ --), ethenylene (--CH═CH--), and ethynylene (--C.tbd.--C--).

The compounds provided by the present invention have many valuable uses as inhibitors of deleterious telomerase activity, most importantly, the use to treat cancer in humans. The pharmaceutical compositions of this invention can be employed in treatment regimens in which cancer cells are killed, in vivo, as demonstrated by the use of telomerase inhibitors of the invention to kill cancer cells ex vivo. Thus, this invention provides therapeutic compositions for treating cancer, and methods for treating cancer in humans and other mammals (e.g., cows, horses, sheep, steer, pigs and animals of veterinary interest such as cats and dogs).

These and other features of the invention will be described in detail below with reference to the associated structures, tables, and accompanying Figure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of tumor mass vs. time for tumors removed from mice exposed to Compound V at a doses of 10 mg/(kg.day) and 25 mg/(kg.day), and a control.

DESCRIPTION OF SPECIFIC EMBODIMENTS

I. Definitions

The term "alkyl" as used herein refers to a straight, branched, or cyclic hydrocarbon chain fragment or radical containing between about one and about twenty carbon atoms, more preferably between about one and about ten carbon atoms (e.g., methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, tert-butyl, cyclobutyl, adamantyl, noradamantyl and the like). Straight, branched, or cyclic hydrocarbon chains having eight or fewer carbon atoms will also be referred to herein as "lower alkyl". The hydrocarbon chains may further include one or more degrees of unsaturation, i.e., one or more double or triple bonds (e.g., vinyl, propargyl, allyl, 2-buten-1-yl, 2-cyclopenten-1-yl, 1,3-cyclohexadien-1-yl, 3-cyclohexen-1-yl and the like). Alkyl groups containing double bonds such as just described will also be referred to to herein as "alkenes". Similarly, alkyl groups having triple bonds will also be referred to herein as "alkynes". However, as used in context with respect to cyclic alkyl groups, the combinations of double and/or triple bonds do not include those bonding arrangements that render the cyclic hydrocarbon chain aromatic.

In addition, the term "alkyl" as used herein further includes one or more substitutions at one or more carbon atoms of the hydrocarbon fragment or radical. Such substitutions include, but are not limited to: aryl; heterocycle; halogen (e.g., trifluoromethyl, --CF₃); nitro (--NO₂); cyano (--CN); hydroxyl (also referred to herein as "hydroxy"), alkoxyl (also referred herein as alkoxy) or aryloxyl (also referred to herein as "aryloxy", --OR); thio or mercapto, alkyl, or arylthio (--SR); amino, alkylamino, arylamino, dialkyl- or diarylamino, or arylalkylamino (--NRR'); aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl or arylalkylaminocarbonyl (--C(O)NRR'); carboxyl, or alkyl- or aryloxycarbonyl (--C(O)OR); aldehyde; aryl- or alkylcarbonyl (RC(O)--); iminyl, or aryl- or alkyliminyl (--C(═NR)--); sulfo (--SO₂ OR); alkyl- or arylsulfonyl (--SO₂ R); hydroximinyl, or aryl- or alkoximinyl (--C(═NOR)--); where R and R' independently are hydrogen, aryl or alkyl as defined herein. Substituents including heterocyclic groups (i.e., heterocycle, heteroaryl, and heteroaralkyl) are defined by analogy to the above-described terms. For example, the term "heterocycleoxy" refers to the group --OR, where R is heterocycle as defined below.

The term "cyclic iminyl" refers to a cyclic group having the general structure shown below ##STR6## where n is 3 or 4 and "C" represents a methylene, methine, or quarternary carbon ring constituent.

The term "halogen" as used herein refers to the substituents fluoro, bromo, chloro, and iodo.

The term "carbonyl" as used herein refers to the functional group --C(O)--. However, it will be appreciated that this group may be replaced with well-known groups that have similar electronic and/or steric character, such as thiocarbonyl (--C(S)--); sulfinyl (--S(O)--); sulfonyl (--SO₂ --), phosphonyl (--PO₂ --), and methylene (--C(CH₂)--). Other carbonyl equivalents will be familiar to those having skill in the medicinal and organic chemical arts.

The term "aryl" as used herein refers to cyclic aromatic carbon chains having twenty or fewer carbon atoms, e.g., phenyl, naphthyl, biphenyl and anthracenyl. One or more carbon atoms of the aryl group may also be substituted with, e.g.: alkyl, aryl, heterocycle, hydroxyl, alkoxyl or aryloxyl; thio or mercapto, alkyl, or arylthio; amino, alkylamino, arylamino, dialkyl- or diarylamino, or arylalkylamino; aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl or arylalkylaminocarbonyl; carboxyl, or alkyl- or aryloxycarbonyl; aldehyde; aryl- or alkylcarbonyl; iminyl, or aryl- or alkyliminyl; sulfo; alkyl- or arylsulfonyl; hydroximinyl, or aryl- or alkoximinyl. In addition, two or more alkyl or heteroalkyl substituents of an aryl group may be combined to form fused aryl-alkyl or aryl-heteroalkyl ring systems (e.g., tetrahydronaphthyl). Substituents including heterocyclic groups (e.g., heterocycleoxy, heteroaryloxy, and heteroaralkylthio) are defined by analogy to the above-described terms.

The term "aralkyl" as used herein refers to an aryl group that is joined to a parent structure by one or more alkyl groups, e.g., benzyl, α-methylbenzyl, phenethyl, and the like.

The term "heterocycle" as used herein refers to a cyclic alkyl group or aryl group as defined above in which one or more carbon atoms have been replaced by a non-carbon atom, especially nitrogen, oxygen, or sulfur. Non-aromatic heterocycles will also be referred to herein as "cyclic heteroalkyl". Aromatic heterocycles are also referred to herein as "heteroaryl". For example, such groups include furyl, tetrahydrofuryl, pyrrolyl, pyrrolidinyl, thienyl, tetrahydrothienyl, oxazolyl, isoxazolyl, triazolyl, thiazolyl, isothiazolyl, pyrazolyl, pyrazolidinyl, oxadiazolyl, thiadiazolyl, imidazolyl, imidazolinyl, pyridyl, pyridazinyl, triazinyl, piperidinyl, morpholinyl, thiomorpholinyl, pyrazinyl, piperazinyl, pyrimidinyl, naphthyridinyl, benzofuranyl, benzothienyl, indolyl, indolinyl, indolizinyl, indazolyl, quinolizinyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, pteridinyl, quinuclidinyl, carbazolyl, acridiniyl, phenazinyl, phenothiazinyl, phenoxazinyl, purinyl, benzimidazolyl and benzthiazolyl.

The above heterocyclic groups may further include one or more substituents at one or more carbon and/or non-carbon atoms of the heteroaryl group, e.g.: alkyl, aryl, heterocycle, hydroxyl, alkoxyl or aryloxyl; thio or mercapto, alkyl- or arylthio; amino, alkylamino, arylamino, dialkyl- or diarylamino, or arylalkylamino; aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl or arylalkylaminocarbonyl; carboxyl, or alkyl- or aryloxycarbonyl; aldehyde; aryl- or alkylcarbonyl; iminyl, or aryl- or alkyliminyl; sulfo; alkyl- or arylsulfonyl; hydroximinyl, or aryl- or alkoximinyl. In addition, two or more alkyl substituents may be combined to form fused heterocycle-alkyl ring systems. Substituents including heterocyclic groups (e.g., heterocycleoxy, heteroaryloxy, and heteroaralkylthio) are defined by analogy to the above-described terms.

The term "heterocyclealkyl" refers to a heterocycle group that is joined to a parent structure by one or more alkyl groups, e.g., 2-piperidylmethyl, and the like. The term "heteroaralkyl" as used herein refers to a heteroaryl group that is joined to a parent structure by one or more alkyl groups, e.g., 2-thienylmethyl, and the like.

II. Telomerase Inhibitors

As noted above, the immortalization of cells involves inter alia the activation of telomerase. More specifically, the connection between telomerase activity and the ability of many tumor cell lines, including skin, connective tissue, adipose, breast, lung, stomach, pancreas, ovary, cervix, uterus, kidney, bladder, colon, prostate, central nervous system (CNS), retina and blood tumor cell lines, to remain immortal has been demonstrated by analysis of telomerase activity (Kim, et al., incorporated herein by reference above). This analysis, supplemented by data that indicates that the shortening of telomere length can provide the signal for replicative senescence in normal cells, see PCT Application No. 93/23572 (incorporated herein by reference above), demonstrates that inhibition of telomerase activity can be an effective anti-cancer therapy. Thus, telomerase activity can prevent the onset of otherwise normal replicative senescence by preventing the normal reduction of telomere length and the concurrent cessation of cell replication that occurs in normal somatic cells after many cell divisions. In cancer cells, where the malignant phenotype is due to loss of cell cycle or growth controls or other genetic damage, an absence of telomerase activity permits the loss of telomeric DNA during cell division, resulting in chromosomal rearrangements and aberrations that lead ultimately to cell death. However, in cancer cells having telomerase activity, telomeric DNA is not lost during cell division, thereby allowing the cancer cells to become immortal, leading to a terminal prognosis for the patient. Agents capable of inhibiting telomerase activity in tumor cells offer therapeutic benefits with respect to a wide variety of cancers and other conditions (e.g., fungal infections) in which immortalized cells having telomerase activity are a factor in disease progression or in which inhibition of telomerase activity is desired for treatment purposes. The telomerase inhibitors of the invention can also be used to inhibit telomerase activity in germ line cells, which may be useful for contraceptive purposes.

Thus, in one aspect, the present invention provides compounds that can serve as an important weapons against many types of malignancies in the war against cancer. In particular, the compounds of the present invention can provide a highly general method of treating many--if not most--malignancies, as demonstrated by the highly varied human tumor cell lines and tumors having telomerase activity. More importantly, the compounds of the present invention can be effective in providing treatments that discriminate between malignant and normal cells to a high degree, avoiding many of the deleterious side-effects present with most current chemotherapeutic regimes which rely on agents that kill dividing cells indiscriminately.

In one aspect, the present invention provides pharmaceutical compositions and methods relating to compounds having the general structure shown as Compound I below: ##STR7## In compound I, X₁ is selected from the group consisting of oxygen, sulfur, sulfone, sulfinyl, and --NR-- where R is hydrogen, alkyl, aryl, and aralkyl. R₁ is --Y_(n) R₆, in which n is an integer between 0 and 10 and each Y_(n) for n greater than 0 independently is methylene, methine, or quarternary carbon. R₆, for any value of n (i.e., n is zero or non-zero), is alkyl, aryl, heterocycle, heteroaryl, aralkyl, heteroaralkyl, alkylcarbonyl, arylcarbonyl, heteroarylcarbonyl, heteroaralkylcarbonyl, aralkylcarbonyl, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, and arylsulfonyl. R₆ can also be a linker L selected from the group consisting of alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl, to which linker between 1 and 3 additional compounds having the structure shown as Compound I above are attached to form thereby homogeneous or heterogeneous poly pyridine aldehydes, acetals, or thioacetals as described in greater detail below. R₂ is hydrogen, alkyl, aryl, hydroxyl, alkoxyl, aryloxyl, halogen, cyano, amino, alkylamino, arylamino, dialkylamino, diarylamino, arylalkylamino, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, or arylsulfonyl. R₃ and R₄ are selected independently from the group consisting of hydrogen, halogen, hydroxyl, aryloxyl, alkoxyl, lower alkyl, aryl, heteroaryl, aralkyl, cyano, carboxyl, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, heteroaralkyl, nitro, amino, alkylamino, arylamino, dialkylamino, diarylamino, and arylalkylamino. Finally, R₅ is selected from the group consisting of bis(alkoxy)methyl, bis(alkylthio)methyl, and --HC═X₂, where X₂ is oxygen or sulfur.

In one embodiment, the present invention provides structures embraced by Compound I in which R₅ is --HC═X₂, where X₂ is sulfur or oxygen, and, more particularly, structures in which X₂ is oxygen to define thereby an aldehyde moiety. In more particular embodiments of Compound I, X₁ is oxygen or sulfur, defining pyridine ethers or pyridine thioethers, and R₂ is cyano (--CN). In still more particular embodiments of Compound I, n is between 1 and 4, and R₆ is aryl, heteroaryl or arylcarbonyl (--C(O)Ar).

In one useful embodiment of Compound I X₂ and R₂ have the identities just described, X₁ is sulfur, n is 1, Y is methylene or methylmethine (--CH(CH₃)--), and R₆ is aryl or heteroaryl. More specifically, useful compounds provided by the present invention include those in which R₆ is aryl. These compounds have the generic structure shown below (Compound II): ##STR8## In Compound II, R₇ -R₁₁ are selected independently from the group consisting of hydrogen, alkyl, aryl, aralkyl, halogen, alkoxyl, aryloxyl, aralkoxyl, heterocycle, and nitro. In addition, adjacent phenyl ring substituents together can form a 5- or 6-membered cyclic alkyl ether or carbocycle ring fused to the phenyl ring of the benzylthioether moiety of the compound.

In some embodiments having the general structure of Compound II above, R₃ and R₄ are hydrogen, and R₇ -R₁₁ are selected independently from the group consisting of hydrogen, methyl, ethyl, 2-phenylethenyl, trifluoromethyl, fluoro, chloro, bromo, phenyl, benzyloxy, trifluoromethoxy, isopropyl, and nitro. In addition, adjacent substituents together can function as points of attachment for the groups --Z₁ --CH₂ --Z₂ --Z₃ -- or --O--(CH₂)_(p) --O--, where Z₁ -Z₃ are selected independently from the group consisting of oxygen, methylene and dimethylmethylene, and p is 1 or 2. More particular embodiments include those in which R₃ and R₄ are hydrogen and R₇ -R₁₁ are selected independently from the group consisting of hydrogen, methyl, phenyl, trifluoromethyl, and chloro. Still more particular substitutions are those in which R₃ and R₄ are hydrogen and R₇, R₈, R₁₀ and R₁₁, are selected independently from the group consisting of hydrogen and chloro and R₉ is selected from the group consisting of hydrogen, trifluoromethyl, phenyl, and chloro. Substitution patterns for several especially useful compounds of the general formula of Compound II where R₃ and R₄ are hydrogen are described in Table I below (Compounds III-VI).

                  TABLE 1                                                          ______________________________________                                         Compound                                                                               R.sub.7  R.sub.8  R.sub.9                                                                               R.sub.10                                                                              R.sub.11                               ______________________________________                                         III     --CH.sub.3                                                                              --CH.sub.3                                                                              --CH.sub.3                                                                            --CH.sub.3                                                                            --CH.sub.3                             IV      --H      --H      --CF.sub.3                                                                            --H    --H                                    V       --H      --H      --Cl   --Cl   --H                                    VI      --Cl     --H      --H    --H    --Cl                                   ______________________________________                                    

Additional compounds of interest having the formula shown for Compound II above include those in which R₉ and R₁₀ are points of attachment for a carbocyclic ring that is fused to the phenyl ring of the benzylthioether moiety. In one embodiment, the carbocyclic ring has the general formula --Z₁ --CH₂ --Z₂ --Z₃ --, where Z₁ -Z₃ are selected independently from the group consisting of oxygen, methylene and dimethylmethylene (--C(CH₃)₂ --). Two embodiments having such a fused ring structure are those in which R₇ and R₈ are hydrogen, R₁₁ is hydrogen or ethyl, and R₉ and R₁₀ are points of attachment for a 1,1,4,4-tetramethylbutylene group (--C(CH₃)₂ --CH₂ --CH₂ --C(CH₃)₂ --), as shown below (Compounds VII and VIII). ##STR9##

Other useful compounds having the general structure of Compound I, are those in which X₁ is sulfur, n is 1, Y is methylene, R₂ is cyano , R₅ is aldehyde, and R₆ is naphthyl, substituted naphthyl, or heteroaryl. In one embodiment in which R₆ is heteroaryl, R₃ and R₄ are hydrogen. In more particular embodiments, R₆ is selected from the group consisting of thienyl, thiazolyl, 1,2,4-oxadiazolyl and benzo b!thiophenyl. Of the latter group of compounds, a particularly useful compound is the one for which R₆ is 2-chloro-5-thienyl (Compound IX). ##STR10##

In still other embodiments of Compound I, X₁ is sulfur, R₂ is cyano, R₅ is aldehyde, n is 1 or 2, Y is methylene, and R₆ is arylcarbonyl. More particular embodiments of these compounds include those in which n is 1, R₃ and R₄ are hydrogen, and R₆ is phenylcarbonyl or substituted phenylcarbonyl (i.e., a phenylcarbonyl moiety in which the phenyl group bears one or more substituents). Of the latter embodiments, those for which R₆ is selected from the group consisting of (3,4-dichlorophenyl)carbonyl (Compound X), (2,4-dichlorophenyl)carbonyl (Compound XI), and (4-chlorophenyl)carbonyl (Compound XII) are particularly useful.

Yet other useful embodiments provided by the present invention include those derivative of Compound I in which R₅ is aldehyde, R₂ is cyano, R₃ and R₄ are hydrogen, X₁ is oxygen, n is 1, Y is methylene, and R₆ is phenyl or substituted phenyl, and especially those derivative for which R₆ is 3,4-dichlorophenyl (Compound XIII).

Compound I of the present invention also embraces structures in which R₆ is a linker L to which linker between one and three additional moieties having the structure of Compound I are bound. Linker L is selected from the group consisting of alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl. In addition to the linkers just recited, L can also be alkoxyalkyl (e.g., --CH₂ --O--CH₂ --), alkylthioalkyl (e.g., --CH₂ --S--CH₂ --), and dialkylamino (e.g., --CH₂ --NR--CH₂ --, where R is hydrogen, alkyl, aryl, or aralkyl). Still more linkers will be apparent to those having skill in the organic and medicinal chemical arts.

In one embodiment of Compound I, n is 1, Y is methylene, and R₆ is a linker L selected from the group consisting of aryl and alkyl. This compound (Compound XIV) has the structure shown below: ##STR11## The subscript m is an integer between 2 and 4. Compounds having the structure of Compound XIV will be recognized as being di-, tri-, and tetrakis- derivatives of Compound I, depending on whether m is 2, 3, or 4, respectively. One particular embodiment of Compound XIV is that in which X₁ is sulfur and R₂ is cyano. A more specific embodiment is that in which R₅ is dialkoxymethyl.

Still other embodiments of Compound XIV are those for which X₁ is sulfur, R₂ is cyano, and R₅ is aldehyde or thioaldehyde. One useful embodiment is that in which R₅ is aldehyde. Other useful embodiments are those in which R₅ is aldehyde and R₃ and R₄ are hydrogen, and those in which X₁ is sulfur, R₅ is aldehyde, R₂ is cyano, R₃ and R₄ are hydrogen, and L is aryl. Particularly useful embodiments of Compound XIV are those for which R₂ -R₅ are as recited above, X₁ is sulfur, m is 2, and L is phenylene, substituted phenylene, naphthylene, substituted naphthylene, anthrylene, or substituted anthrylene. Of these compounds, those for which L is selected from the group consisting of 2,4-dimethyl-1,5-phenylene (Compound XV), 2,4,6-trimethyl-1,3-phenylene (Compound XVI), 1,3-phenylene (Compound XVII), 1,2-phenylene (Compound XVIII), 1,4-phenylene (Compound XIX), 3,4,5,6-tetramethyl-1,2-phenylene (Compound XX), 2,5-dichloro-1,4-phenylene (Compound XXI), 2,3,4,6-tetramethyl-1,5-phenylene (Compound XXII), 2,5-dimethyl-1,4-phenylene (Compound XXIII), 2,2'-biphenylene (Compound XXIV), 4,4'-dibromo-2,2'-biphenylene (Compound XXV), 2,3-naphthylene (Compound XXVI), 1,8-naphthylene (Compound XXVII), 2,3,5,6-tetrachloro-1,4-phenylene (Compound XXVIII), 9,10-anthrylene (Compound XXIX), and 1,2-naphthylene (Compound XXX) have especially useful properties.

Still other embodiments of Compound XIV which have useful telomerase-inhibiting properties are those for which m is 3 or 4 and L is substituted or unsubstituted benzenetriyl or benzenetetrayl, and, in particular, those compounds shown below (Compounds XXXI-XXXIII). ##STR12##

Yet other useful embodiments of Compound XIV are those for which m is 2, R₂ cyano, R₃ and R₄ are hydrogen, X₁ is sulfur, R₅ is aldehyde, and L is alkyl, especially those for which L is selected from the group consisting of ethylene (--CH₂ --CH₂ --, Compound XXXIV), ethenylene (--CH═CH--, Compound XXXV), and ethynylene (--C.tbd.C--, Compound XXXVI). Again, those of skill in the art will recognize that still other linkers can be employed without departing from the present invention.

III. Synthesis of Telomerase Inhibitors

The compounds of the present invention can be synthesized using techniques and materials known to those of skill in the art, such as described, for example, in March, ADVANCED ORGANIC CHEMISTRY 4^(th) Ed., (Wiley 1992); Carey and Sundberg, ADVANCED ORGANIC CHEMISTRY 3^(rd) Ed., Vols. A and B (Plenum 1992), and Green and Wuts, PROJECTIVE GROUPS IN ORGANIC SYNTHESIS 2^(nd) Ed. (Wiley 1991), each of which is incorporated herein by reference. Starting materials for the compounds of the invention may be obtained using standard techniques and commercially available precursor materials, such as those available from Aldrich Chemical Co. (Milwaukee, Wis.), Sigma Chemical Co. (St. Louis, Mo.), Lancaster Synthesis (Windham, N.H.), Apin Chemicals, Ltd. (New Brunswick, N.J.), Ryan Scientific (Columbia, S.C.), Maybridge (Cornwall, England) and Trans World Chemicals (Rockville, Md.).

The procedures described herein for synthesizing the compounds of the invention may include one or more steps of protection and deprotection (e.g., the formation and removal of acetal groups). In addition, the synthetic procedures disclosed below can include various purifications, such as column chromatography, flash chromatography, thin-layer chromatography (TLC), recrystallization, distillation, high-pressure liquid chromatography (HPLC) and the like. Also, various techniques well known in the chemical arts for the identification and quantification of chemical reaction products, such as proton and carbon-13 nuclear magnetic resonance (¹ H and ¹³ C NMR), infrared and ultraviolet spectroscopy (IR and UV), X-ray crystallography, elemental analysis (EA), HPLC and mass spectroscopy (MS) can be used as well. Methods of protection and deprotection, purification and identification and quantification are well known in the chemical arts.

Compounds of the class represented by Compound I can be synthesized using the following general procedure (Scheme 1). The use of the substituent identifiers R and R' is merely to indicate the presence of one or more substituents at the position or moiety indicated. The values of R and R' shown in Scheme 1 below can be determined by reference to the specific moieties described above in connection with the structure of Compound I. ##STR13##

With the appropriately substituted derivative of commercially available 2-thio-3-cyano-6-(dimethoxymethyl)pyridine 1, reaction with an appropriate alkylating agent or other nucleophile under basic conditions (e.g., potassium carbonate (K₂ CO₃) in dimethylformamide (DMF)) followed by addition of R'X where X is a halide or other suitable leaving group such as tosyl provides the desired dialkoxymethyl thioether 2. Removal of the acetal group using standard conditions (e.g., p-toluenesulfonic acid in benzene), provides the desired aldehyde 3.

Formation of the above-described di-, tri-, or tetrakispyridylthioethers is accomplished by analogy to the reactions illustrated in Scheme I above, in which R' is a nucleophile corresponding to the desired linker L and alkyl chain Y_(n). For example, where n is 1, Y is methylene and L is phenyl, one equivalent of starting dimethoxymethylpyridine thiol 1 is combined with the nucleophile R' for each leaving group available on the linker. Following the coupling of the linker to the starting dimethoxymethylpyridine thiol 1, the dimethoxymethyl group of each of the linked pyridylthioethers is converted to the corresponding aldehyde 3. For example, reaction of two equivalents of 1 (R═H) with one equivalent of α,α'-dichloroxylene as described above for Scheme 1 provides the corresponding dialdehyde.

Protocols from which the individual compounds described above can be synthesized are provided in the Examples below.

IV. Anti-Tumor Activity of the Telomerase Inhibitors of the Invention

The compounds of the present invention demonstrate inhibitory activity against telomerase in vitro and in vivo, as has been and can be demonstrated as described below. As used herein, the term "in vitro" refers to tests performed using living cells in tissue culture. Such procedures are also known as "ex vivo".

One method used to identify compounds of the invention that inhibit telomerase activity involves placing cells, tissues, or preferably a cellular extract or other preparation containing telomerase in contact with several known concentrations of a test compound in a buffer compatible with telomerase activity. The level of telomerase activity for each concentration of test compound is measured and the IC₅₀ (the concentration of the test compound at which the observed activity for a sample preparation was observed to fall one-half of its original or a control value) for the compound is determined using standard techniques. Other methods for determining the inhibitory concentration of a compound of the invention against telomerase can be employed as will be apparent to those of skill in the art based on the disclosure herein.

IC₅₀ values for several of the compounds of the present invention were determined using known methods. The values reported in Table 2 below are only approximate values; more exact IC₅₀ values can be obtained by repetitive testing.

                  TABLE 2                                                          ______________________________________                                         Compound  IC.sub.50 (μM)                                                                         Compound    IC.sub.50 (μM)                             ______________________________________                                         III       9.0        XXI         <3.2                                          IV        18.0       XXII        4.0                                           V         4.5        XXIII       7.0                                           VI        7.0        XXIV        <3.2                                          VII       8.0        XXV         <3.2                                          VIII      21.0       XXVI        6.0                                           IX        5.0        XXVII       <3.2                                          X         10.9       XXVIII      <3.2                                          XI        27.0       XXIX        7.0                                           XII       15.1       XXX         7.0                                           XIII      12.8       XXXI        <3.2                                          XV        <3.2       XXXII       <3.2                                          XVI       <3.2       XXXIII      <3.2                                          XVII      <3.2       XXXIV       7.0                                           XVIII     6.0        XXXV        10.0                                          XIX       5.0        XXXVI       5.0                                           XX        <3.2                                                                 ______________________________________                                    

As shown in Table I, all of the compounds have anti-telomerase activity (i.e., IC₅₀ <50.0 μM). Several of the compounds of the invention (V, IX, XV-XVII, XIX-XXII, XXIV, XXV, XXVII, XXVIII, XXXI-XXXIII, and XXXVI) are especially potent telomerase inhibitors, having approximate IC₅₀ values of less than about 5.0 μM. In addition, Compound V was also found to induce cleavable complex formation in Topoisomerase II with a level of activity greater than the well-known anti-tumor agents adriamycin and mitoxantrone (see below).

Compounds of the invention also demonstrate specificity for telomerase activity ex vivo. In on experiment, Compound V was administered to IMR-90, OVCAR-5, and SK-OV-3 cell samples at a concentration one quarter that of its IC₅₀ for telomerase. The effects of Compound V on the activity of Topoisomerase II, Single-Strand Binding Protein, and Terminal Transferase were then determined using standard methodologies. Compound V was found to be more specific for telomerase by a factor of about 5 (see below).

In vivo testing was also performed using a mouse xenograft model in which OVCAR-5 tumor cells were grafted onto nude mice. As discussed below, mice treated with Compound V had tumor masses that, on average, increased for a period following the initial dosing, but began to level with continuing treatment. In contrast, mice treated with a control (DMSO) are expected to have tumor masses that continue to increase. Compound V of the invention was therefore found to be highly effective in halting the growth of tumor cells in vitro and in vivo.

From the foregoing those skilled in the art will appreciate that the present invention also provides methods for selecting treatment regimens involving administration of a compound of the invention. For such purposes, it may be helpful to perform a TRF analysis in which DNA from tumor cells is analyzed by digestion with restriction enzymes specific for sequences other than the telomeric (T₂ AG₃)_(N) sequence. Following digestion of the DNA, gel electrophoresis is performed to separate the restriction fragments according to size. The separated fragments are then probed with nucleic acid probes specific for telomeric sequences to determine the lengths of the telomeres of the cells in the sample. By measuring the length of telomeric DNA, one can estimate how long a telomerase inhibitor should be administered and whether other methods of therapy (e.g., surgery, chemotherapy and/or radiation) should also be employed. In addition, during treatment, one can test cells to determine whether a decrease in telomere length over progressive cell divisions is occurring to demonstrate treatment efficacy.

V. Telomerase Inhibiting Compositions and Methods for Treating Diseases With the Same

The present invention also provides pharmaceutical compositions for treating cancer and other conditions in which inhibition of telomerase is an effective therapy. These compositions include a therapeutically effective amount of a telomerase inhibiting compound of the invention in a pharmaceutically acceptable carrier or salt. In one preferred embodiment, the present invention provides a composition effective for treating cancer in a mammal. The composition includes a therapeutically effective amount of a compound having the structure of Compound I in a pharmaceutically acceptable carrier.

The compounds of the present invention can also be used to treat hyperproliferative diseases of any type in which telomerase activity is found in the hyperproliferating cells. Such diseases include, but are not limited to, cancer, psoriasis, Marfan's syndrome, benign hyperplasia, and the like. Also, in some cases it might be useful to combine telomerase inhibitors, such as the compounds provided in the present invention, with other therapeutic agents. Such therapeutic agents can come from any class or other type of compound. For treating cancer, for example, one can combine a telomerase inhibitor of the invention with a compound capable of affecting chromatin structure, including inhibitors of histone deacetylase such as sodium butyrate, and trichostatin A. In addition, Topoisomerase II inhibitors such as m-AMSA, amsacrine, and atroposida are believed to affect chromatin. Thus, compounds of the present invention that display inhibitory activity with respect to Topoisomerase II, such as Compound V, can also be used affect chromatin structure. The choice of such combinations will depend on various factors including, but not limited to, the type of disease, the age and general health of the patient, the aggressiveness of disease progression, the TRF length and telomerase activity of the diseased cells to be treated and the ability of the patient to tolerate the agents that comprise the combination. In addition, in some cases it may be advisable to combine a telomerase inhibiting agent of the invention with one or more agents that treat the side effects of a disease, e.g., an analgesic, or agents effective to stimulate the patient's own immune response (e.g., colony stimulating factor).

As an example of one such therapeutic combination, a pharmaceutical formulation comprises a telomerase inhibitor of the invention and an anti-angiogenesis agent, such as fumagillin, fumagillin derivatives, or AGM-1470. The latter compound is available from Takeda Chemical Industries, Ltd., while the former compounds are described in Ingber, et al., 6 Dec. 1990, "Synthetic analogues of fumagillin that inhibit angiogenesis and suppress tumor growth", Nature 348:555-557, incorporated herein by reference for all purposes. Other combinations may include, but are not limited to, a telomerase inhibitor of the invention in addition to one or more antineoplastic agents or adjuncts (e.g., folinic acid or mesna).

Antineoplastic agents suitable for combination with the compounds of the present invention include, but are not limited to, alkylating agents including alkyl sulfonates such as busulfan, improsulfan and piposulfan; aziridines, such as a benzodizepa, carboquone, meturedepa and uredepa; ethylenimines and methylmelamines such as altretamine, triethylenemelamine, triethylenephosphoramide, triethylenethiophosphoramide and trimethylolmelamine; nitrogen mustards such as chlorambucil, chlornaphazine, cyclophosphamide, estramustine, iphosphamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichine, phenesterine, prednimustine, trofosfamide, and uracil mustard; nitroso ureas, such as carmustine, chlorozotocin, fotemustine, lomustine, nimustine and ranimustine. Additional agents include dacarbazine, mannomustine, mitobronitol, mitolactol and pipobroman. Still other classes of relevant agents include antibiotics, hormonal antineoplastics and antimetabolites. Yet other combinations will be apparent to those of skill in the art.

Additional agents suitable for combination with the compounds of the present invention include protein synthesis inhibitors such as abrin, aurintricarboxylic acid, chloramphenicol, colicin E3, cycloheximide, diphtheria toxin, edeine A, emetine, erythromycin, ethionine, fluoride, 5-fluorotryptophan, fusidic acid, guanylyl methylene diphosphonate and guanylyl imidodiphosphate, kanamycin, kasugamycin, kirromycin, and O-methyl threonine. Additional protein synthesis inhibitors include modeccin, neomycin, norvaline, pactamycin, paromomycine, puromycin, ricin, α-sarcin, shiga toxin, showdomycin, sparsomycin, spectinomycin, streptomycin, tetracycline, thiostrepton and trimethoprim. Inhibitors of DNA synthesis, including alkylating agents such as dimethyl sulfate, mitomycin C, nitrogen and sulfur mustards, MNNG and NMS; intercalating agents such as acridine dyes, actinomycins, adriamycin, anthracenes, benzopyrene, ethidium bromide, propidium diiodide intertwining agents such as distamycin and netropsin, can also be combined with compounds of the present invention in pharmaceutical compositions. DNA base analogs such as acyclovir, adenine β-1-D-arabinoside, amethopterin, aminopterin, 2-aminopurine, aphidicolin, 8-azaguanine, azaserine, 6-azauracil, 2'-azido-2'-deoxynucleosides, 5-bromodeoxycytidine, cytosine β-1-D-arabinoside, diazooxynorleucine, dideoxynucleosides, 5-fluorodeoxycytidine, 5-fluorodeoxyuridine, 5-fluorouracil, hydroxyurea and 6-mercaptopurine also can be used in combination therapies with the compounds of the invention. Topoisomerase inhibitors, such as coumermycin, nalidixic acid, novobiocin and oxolinic acid, inhibitors of cell division, including colcemide, colchicine, vinblastine and vincristine, and RNA synthesis inhibitors including actinomycin D, α-amanitine and other fungal amatoxins, cordycepin (3'-deoxyadenosine), dichlororibofuranosyl benzimidazole, rifampicine and streptovaricin and streptolydigin also can be combined with the compounds of the invention to provide pharmaceutical compositions.

In some cases it may be advisable to combine a telomerase inhibiting compound of the invention with other agents and therapeutic regimens that are effective at reducing tumor size (e.g. radiation, surgery, chemotherapy and/or hormonal treatments). Alternatively, one or more telomerase-inhibiting compounds of the present invention can be combined with one or more compounds that demonstrate activity with respect to Topoisomerase II, as such compounds are known to be effective oncolytic agents. Indeed, it has been found that certain compounds of the present invention, e.g., Compound V, demonstrate inhibitory activity with respect to Topoisomerase II. Thus, in some cases a compound of the present invention may be administered to a cancer patient for its oncolytic properties in addition to the compound's telomerase-inhibiting properties. In other cases a compound of the invention may be administered solely for its oncolytic properties.

In another embodiment, the present invention includes compounds and compositions in which a telomerase inhibitor is either combined with or covalently bound to a cytotoxic agent bound to a targeting agent, such as a monoclonal antibody (e.g., a murine or humanized monoclonal antibody). It will be appreciated that the latter combination may allow the introduction of cytotoxic agents into cancer cells with greater specificity. Thus, the active form of the cytotoxic agent (i.e., the free form) will be present only in cells targeted by the antibody. Of course, the telomerase inhibitors of the invention may also be combined with monoclonal antibodies that have therapeutic activity against cancer.

In general, a suitable effective dose of a compound of the invention will be in the range of 0.001 to 1000 milligram (mg) per kilogram (kg) of body weight of the recipient per day, preferably in the range of 0.001 to 100 mg per kg of body weight per day, more preferably between about 0.1 and 100 mg per kg of body weight per day and still more preferably in the range of between 0.1 to 10 mg per kg of body weight per day. The desired dosage is preferably presented in one, two, three, four, or more subdoses administered at appropriate intervals throughout the day. These subdoses can be administered as unit dosage form, for example, containing 5 to 10,000 mg, preferably 10 to 1000 mg of active ingredient per unit dosage from. Preferably, the dosage is presented once per day at a dosing at least equal to TID.

The composition used in these therapies can be in a variety of forms. These include, for example, solid, semi-solid, and liquid dosage forms, such as tablets, pills, powders, liquid solutions or suspensions, liposomes, and injectable and infusible solutions. The preferred form depends on the intended mode of administration and therapeutic application. The compositions also preferably include conventional pharmaceutically acceptable carriers and adjuvants, as is well known to those of skill in the art. See, e.g., REMINGTON'S PHARMACEUTICAL SCIENCES, Mack Publishing Co.: Easton, Pa., 17th Ed. (1985). Preferably, administration will be by oral or parenteral (including subcutaneous, intramuscular, intravenous, and intradermal) routes. More preferably, the route of administration will be oral. The therapeutic methods and agents of this invention can of course be used concomitantly or in combination with other methods and agents for treating a particular disease or disease condition.

While it is possible to administer the active ingredient of this invention alone, it is preferable to present a therapeutic agent as part of a pharmaceutical formulation or composition. The formulations of the present invention comprise at least one telomerase activity-inhibiting compound of this invention in a therapeutically or pharmaceutically effective dose together with one or more pharmaceutically or therapeutically acceptable carriers and optionally other therapeutic ingredients. Various considerations for preparing such formulations are described, e.g., in Gilman et al. (eds.) GOODMAN AND GILMAN'S: THE PHARMACOLOGICAL BASES OF THERAPEUTICS, 8th Ed., Pergamon Press (1990); and REMINGTON'S supra, each of which is incorporated herein by reference for all purposes. Methods for administration are discussed therein, e.g., for oral, intravenous, intraperitoneal, intramuscular, and other forms of administration. Generally, oral administration is preferred.

Typically, methods for administering pharmaceutical compositions will be either topical, parenteral, or oral administration methods for prophylactic and/or therapeutic treatment. Oral administration is a preferred. The pharmaceutical compositions can be administered in a variety of unit dosage forms depending upon the method of administration. As noted above, unit dosage forms suitable for oral administration include powders, tablets, pills, and capsules.

One can use topical administration to deliver a compound of the invention by percutaneous passage of the drug into the systemic circulation of the patient. The skin sites include anatomic regions for transdermally administering the drug, such as the forearm, abdomen, chest, back, buttock, and mastoidal area. The compound is administered to the skin by placing on the skin either a topical formulation comprising the compound or a transdermal drug delivery device that administers the compound. In either embodiment, the delivery vehicle is designed, shaped, sized, and adapted for easy placement and comfortable retention on the skin.

A variety of transdermal drug delivery devices can be employed with the compounds of this invention. For example, a simple adhesive patch comprising a backing material and an acrylate adhesive can be prepared. The drug and any penetration enhancer can be formulated into the adhesive casting solution. The adhesive casting solution can be cast directly onto the backing material or can be applied to the skin to form an adherent coating. See, e.g., U.S. Pat. Nos. 4,310,509; 4,560,555; and 4,542,012.

In other embodiments, the compound of the invention will be delivered using a liquid reservoir system drug delivery device. These systems typically comprise a backing material, a membrane, an acrylate based adhesive, and a release liner. The membrane is sealed to the backing to form a reservoir. The drug or compound and any vehicles, enhancers, stabilizers, gelling agents, and the like are then incorporated into the reservoir. See, e.g., U.S. Pat. Nos. 4,597,961; 4,485,097; 4,608,249; 4,505,891; 3,843,480; 3,948,254; 3,948,262; 3,053,255; and 3,993,073.

Matrix patches comprising a backing, a drug/penetration enhancer matrix, a membrane, and an adhesive can also be employed to deliver a compound of the invention transdermally. The matrix material typically will comprise a polyurethane foam. The drug, any enhancers, vehicles, stabilizers, and the like are combined with the foam precursors. The foam is allowed to cure to produce a tacky, elastomeric matrix which can be directly affixed to the backing material. See, e.g., U.S. Pat. Nos. 4,542,013; 4,460,562; 4,466,953; 4,482,534; and 4,533,540.

Also included within the invention are preparations for topical application to the skin comprising a compound of the invention, typically in concentrations in the range from about 0.001 % to 10%, together with a non-toxic, pharmaceutically acceptable topical carrier. These topical preparations can be prepared by combining an active ingredient according to this invention with conventional pharmaceutical diluents and carriers commonly used in topical dry, liquid, and cream formulations. Ointment and creams may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or gelling agents. Such bases may include water and/or an oil, such as liquid paraffin or a vegetable oil, such as peanut oil or castor oil. Thickening agents that may be used according to the nature of the base include soft paraffin, aluminum stearate, cetostearyl alcohol, propylene glycol, polyethylene glycols, woolfat, hydrogenated lanolin, beeswax, and the like.

Lotions may be formulated with an aqueous or oily base and will, in general, also include one or more of the following: stabilizing agents, emulsifying agents, dispersing agents, suspending agents, thickening agents, coloring agents, perfumes, and the like. Powders may be formed with the aid of any suitable powder base, e.g., talc, lactose, starch, and the like. Drops may be formulated with an aqueous base or non-aqueous base also comprising one or more dispersing agents, suspending agents, solubilizing agents, and the like. Topical administration of compounds of the invention may also be preferred for treating diseases such as skin cancer and fungal infections of the skin (pathogenic fungi typically express telomerase activity).

The topical pharmaceutical compositions according to this invention may also include one or more preservatives or bacteriostatic agents, e.g., methyl hydroxybenzoate, propyl hydroxybenzoate, chlorocresol, benzalkonium chlorides, and the like. The topical pharmaceutical compositions also can contain other active ingredients such as antimicrobial agents, particularly antibiotics, anesthetics, analgesics, and antipruritic agents.

The compounds of the present invention can also be delivered through mucosal membranes. Transmucosal (i.e., sublingual, buccal, and vaginal) drug delivery provides for an efficient entry of active substances to systemic circulation and reduces immediate metabolism by the liver and intestinal wall flora. Transmucosal drug dosage forms (e.g., tablet, suppository, ointment, pessary, membrane, and powder) are typically held in contact with the mucosal membrane and disintegrate and/or dissolve rapidly to allow immediate systemic absorption. Note that certain such routes may be used even where the patient is unable to ingest a treatment composition orally. Note also that where delivery of a telomerase inhibitor of the invention would be enhanced, one can select a composition for delivery to a mucosal membrane, e.g., in cases of colon cancer one can use a suppository to deliver the telomerase inhibitor.

For delivery to the buccal or sublingual membranes, typically an oral formulation, such as a lozenge, tablet, or capsule, will be used. The method of manufacture of these formulations is known in the art, including, but not limited to, the addition of the pharmacological agent to a pre-manufactured tablet; cold compression of an inert filler, a binder, and either a pharmacological agent or a substance containing the agent (as described in U.S. Pat. No. 4,806,356); and encapsulation. Another oral formulation is one that can be applied with an adhesive, such as the cellulose derivative hydroxypropyl cellulose, to the oral mucosa, for example as described in U.S. Pat. No. 4,940,587. This buccal adhesive formulation, when applied to the buccal mucosa, allows for controlled release of the pharmacological agent into the mouth and through the buccal mucosa.

Parenteral administration is generally characterized by injection, either subcutaneously, intramuscularly, or intravenously. Thus, this invention provides compositions for intravenous administration that comprise a solution of a compound of the invention dissolved or suspended in an acceptable carrier. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions. Suitable excipients are, for example, water, buffered water, saline, dextrose, glycerol, ethanol, or the like. These compositions will be sterilized by conventional, well known sterilization techniques, such as sterile filtration. The resulting solutions can be packaged for use as is or lyophilized, the lyophilized preparation being combined with a sterile solution prior to administration. In addition, if desired, the pharmaceutical compositions to be administered may also contain minor amounts of non-toxic auxiliary substances, such as wetting or emulsifying agents, pH buffering agents and the like, such as for example, sodium acetate, sorbitan monolaurate, triethanolamine oleate, etc. Such formulations will be useful in treating ovarian cancers.

Another method of parenteral administration employs the implantation of a slow-release or sustained-release system, such that a constant level of dosage is maintained. See, e.g., U.S. Pat. No. 3,710,795, incorporated herein by reference.

Liquid pharmaceutically administrable compositions can, for example, be prepared by dissolving, dispersing, etc., an active compound as defined above and optional pharmaceutical adjuvants in an excipient, such as, for example, water, saline, aqueous dextrose, glycerol, ethanol, olive oil, and other lipophilic solvents, and the like, to form a solution or suspension. If desired, the pharmaceutical composition to be administered may also contain minor amounts of nontoxic auxiliary substances, such as wetting or emulsifying agents, pH buffering agents, and the like, for example, sodium acetate, sorbitan monolaurate, triethanolamine sodium acetate, triethanolamine oleate, etc. Actual methods of preparing such dosage forms are known and will be apparent to those skilled in this art; for example, see REMINGTON'S PHARMACEUTICAL SCIENCES, supra. The composition or formulation to be administered will contain an effective amount of an active compound of the invention.

For solid compositions, conventional nontoxic solid carriers can be used and include, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharin, talcum, cellulose, glucose, sucrose, magnesium carbonate, and the like. For oral administration, a pharmaceutically acceptable nontoxic composition is formed by incorporating any of the normally employed excipients, such as those carriers previously listed, and generally 0.1-95% of active ingredient, preferably about 20%.

The compositions containing the compounds of the invention can be administered for prophylactic and/or therapeutic treatments. In therapeutic applications, compositions are administered to a patient already suffering from a disease, as described above, in an amount sufficient to cure or at least partially arrest the symptoms of the disease and its complications. An amount adequate to accomplish this is defined as a "therapeutically effective amount or dose." Amounts effective for this use will depend on the severity of the disease and the weight and general state of the patient.

In addition to internal (in vivo) administration, the compounds and compositions of the invention may be applied ex vivo to achieve therapeutic effects, as for example, in the case of a patient suffering from leukemia. In such an application, cells to be treated, e.g., blood or bone marrow cells, are removed from a patient and treated with a pharmaceutically effective amount of a compound of the invention. The cells are returned to the patient following treatment. Such a procedure can allow for exposure of cells to concentrations of therapeutic agent for longer periods or at higher concentrations than otherwise available.

Once improvement of the patient's conditions has occurred, as, for example, by the occurrence of remission in the case of a cancer patient, a maintenance dose is administered, if necessary. Subsequently, the dosage or the frequency of administration, or both, can be reduced, as a function of the systems, to a level at which the improved condition is retained. When the symptoms have been alleviated to the desired level, treatment can cease. Patients can, however, require additional treatment upon any recurrence of the disease symptoms.

In prophylactic applications (e.g. chemoprevention), compositions containing the compounds of the invention are administered to a patient susceptible to or otherwise at risk of a particular disease. Such an amount is defined to be a "prophylactically effective amount or dose." In this use, the precise amounts again depend on the patient's state of health and weight.

As will be apparent to those of skill in the art upon reading of this disclosure, the present invention provides valuable reagents relating to human telomerase. The above description of necessity provides a limited and merely illustrative sampling of specific compounds, and should not be construed as limiting the scope of the invention. Other features and advantages of the invention will be apparent from the following examples and claims.

EXAMPLES

The following examples describe specific aspects of the invention to illustrate the invention and also provide a description of the methods used to identify and test compounds that inhibit the activity of telomerase to aid those of skill in the art in understanding and practicing the invention. The examples should not be construed as limiting the invention, in any manner.

A. Chemical Syntheses

The following General Procedures illustrate the synthesis of the compounds in the class defined by the structure of Compound I.

General Procedure A: Synthesis of 6-Dimethoxymethyl-3-Cyano-2-Thioetherpyridines

The following demonstrates the synthesis of Compound 2 of Scheme 1. Into a round-bottom flask equipped with a magnetic stir bar and under a positive pressure of nitrogen were placed 3-cyano-2-mercaptopyridine-6-carboxaldehyde dimethyl acetal (1.0513 g, 5.0 mmol), DMF (5 ml), K₂ CO₃ (0.7602 g, 5.5 mmol), and the corresponding alkylating agent (5.2 mmol). The heterogeneous mixture was stirred at room temperature for 3 hr. The reaction mixture was poured into ice/H₂ O (50 ml) and extracted twice with ethyl acetate (EtOAc.) The combined organic layers were washed with saturated sodium chloride (NaCl, brine), dried over magnesium sulfate (MgSO₄), filtered, and the solvent removed by rotary evaporation to yield the coupled product. Isolated yields range from 87-96% The product was analyzed by ¹ H NMR and TLC.

General Procedure B: Acetal Deprotection of 6-Dimethoxymethyl-3-Cyano-2-Thioetherpyridines

The following demonstrates the conversion of Compound 2 of Scheme 1 into Compound 3 of the same Scheme. Into a round-bottom, three-necked flask equipped with a magnetic stir bar, thermometer, reflux condenser, and under a positive pressure of nitrogen, were placed the corresponding dimethyl acetal (5.0 mmol), benzene (60 ml), and p-toluenesulfonic acid (1.9975 g, 10.5 mmol). The mixture was refluxed at 73°-78° C. for 48 hours (h). The reaction was quenched by pouring the reaction mixture into saturated aqueous (sat. aq.) sodium bicarbonate (NaHCO₃) and then extracted twice with methylene chloride. The combined organic layers were washed with sat. NaCl (brine), dried over MgSO₄, filtered, and the solvent removed by rotary evaporation to yield the desired aldehyde. The product was analyzed by H¹ NMR and TLC.

General Procedure C: Deprotection of Dimethoxyacetal Pyridine Thioethers

This procedure also illustrates the conversion of Compound 2 of Scheme 1 into Compound 3 of that Scheme. Into a round bottom, three-necked flask equipped with a magnetic stir bar, thermometer and under a positive nitrogen pressure, were introduced the corresponding acetal (7.0 mmol) and chloroform (CHCl₃, 63 mL). To this mixture was added aqueous trifluoroacetic acid (TFA/H₂ O, 31 mL/31 mL) at 0° C. The mixture was stirred vigorously at 35° C. until completion, as determined by TLC analysis (3-78 h.) The reaction was quenched with sat. aq. NaHCO₃ and the solution extracted twice with EtOAc. The combined organic layers were washed with sat. aq. NaCl (brine), then dried over sodium sulfate (Na₂ SO₄) and filtered. The solvent was removed by rotary evaporation, and the product analyzed by ¹ H NMR and TLC.

B. Anti-tumor Activity

1. Ex vivo Studies

a. Reduction of Telomere Length in Tumor Cells

Colonies of the ovarian tumor cell lines OVCAR-5, SK-OV-3 and IMR-90 cells were prepared using standard methods and materials. In one test, the colonies were prepared by seeding 15-centimeter dishes with about 10⁶ cells in each dish. The dishes were incubated to allow the cell colonies to grow to about 80% confluence, at which time each of the colonies was divided into two groups. One group was exposed to a subacute dose of Compound V (5 μM) 4-8 hours after plating following the split; the other group was exposed to a DMSO control.

Each group was then allowed to continue to divide, and the groups were split evenly again (near confluence). The same number of cells were seeded for continued growth. The compound or control was added every second day to the samples at the same concentration delivered initially (5 μM). Compound V was found to induce senescence in IMR-90 cells approximately 5 period doublings earlier than cells treated with the DMSO control. A small effect was noted for OVCAR-5 cell growth. No effect was seen on SK-OV-3 cells.

b. Topoisomerase II Inhibition

Compound V was tested for its ability to target Topoisomerase II in a standard enzyme-mediated DNA cleavage assay. The well known anti-tumor agent VP-16 was used as a positive control. The results of the assay demonstrated that Compound V targeted Topoisomerase II, as demonstrated by the detection of Topoisomerase II-mediated DNA cleavage by the detection of linear DNA in an agarose gel. The amount of linear DNA was proportional to the concentration of Compound V used in the experiment. These results indicated that Compound V has one fifth the activity of VP-16, but is a stronger Topoisomerase II-targeting antitumor agent than the known Topoisomerase II-targeting agents adriamycin and mitoxantrone.

c. Specificity

Compound V was screened for activity (IC₅₀) against telomerase and several enzymes having nucleic acid binding or modifying activities related to telomerase using standard techniques. The enzymes screened included Telomerase, Topoisomerase II, Terminal Transferase and Single-Stranded DNA Binding Protein (SSB). The test compound was found to have at least a 5-fold lower specificity for Topoisomerase II, Terminal Transferase and Single-Stranded DNA Binding Protein (SSB) as compared to Telomerase. Thus, Compound V demonstrated high specificity for telomerase.

d. Cytotoxicity

The XTT assay for cytotoxicity was performed using the ovarian tumor cells lines IMR-90, OVCAR-5 and SK-OV-3. Cells from the normal human cell line BJ were used as a control. The cell lines used in the assay were exposed to Compound V of the invention for 72 hours at concentrations ranging from 3 μM to 1,000 μM. During this period, the optical density (OD) of the samples was determined for light at 540 nanometers (nm). The LD₅₀ (the concentration of test compound at which half of the sample population dies) for each of the cells lines tested was 5 μM, 15 μM, and 10 μM, respectively.

2. In vivo Studies

A human tumor xenograft model in which OVCAR-5 tumor cells were grafted into nude mice was constructed using standard techniques and materials. The mice were divided into two groups. One group was treated intraperitoneally with Compound V. The other group was treated with a control comprising DMSO and phosphate buffer solution (PBS). The average tumor mass for mice in each group was determined periodically following the xenograft using standard methods and materials.

Compound V was found to cause statistically significant slowing of tumor growth (p<0.05, unpaired t-test) as compared to vehicle alone. These results are illustrated in FIG. 1, which shows that while tumors in mice treated with vehicle alone or with Compound V at a dose of 10 mg/(kg.day) were not affected, the increase in tumor weight in mice treated with Compound V at a dose of 25 mg/(kg.day) practically ceased after about 50 days.

Thus, the present invention provides novel compounds, compositions and methods for inhibiting telomerase activity and treating disease states in which telomerase activity has deleterious effects, especially cancer. The compounds of the invention provide a highly selective and effective treatment for malignant cells that require telomerase activity to remain immortal; yet, without affecting non-malignant cells.

Although certain embodiments and examples have been used to describe the present invention, it will be apparent to those of skill in the art that changes may be made to those described embodiments and examples without departing from the scope or spirit of the invention or the following claims. 

What is claimed:
 1. A telomerase inhibiting compound having the structure: ##STR14## and the pharmaceutically acceptable salts thereof, wherein: X₁ is selected from the group consisting of oxygen, sulfur, sulfone, sulfinyl;R₁ is --Y_(n) R₆, where n is an integer between 0 and 10 and each Y_(n) for n greater than 0 independently is methylene, methine, or quarternary carbon, and R₆, for any value of n, is alkyl, aryl, heterocycle, heteroaryl, aralkyl, heteroaralkyl, alkylcarbonyl, arylcarbonyl, heteroalkylcarbonyl, heteroaralkylcarbonyl, aralkylcarbonyl, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfonyl, arylsulfonyl, alkylsulfinyl, arylsulfinyl, or a linker L selected from the group consisting of alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl to which linker between 1 and 3 additional compounds having the structure shown above are attached; R₂ is hydrogen, alkyl, aryl, hydroxyl, alkoxyl, aryloxyl, halogen, cyano, amino, alkylamino, arylamino, dialkylamino, diarylamino, arylalkylamino, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy, aldehyde, sulfo, alkylsulfinyl, arylsulfinyl, alkylsulfonyl, or arylsulfonyl; R₃ and R₄ are selected independently from the group consisting of hydrogen, halogen, hydroxyl, aryloxyl, alkoxyl, lower alkyl, aryl, heteroaryl, aralkyl, cyano, carboxyl, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, heteroaralkyl, nitro, amino, alkylamino, arylamino, dialkylamino, diarylamino, and arylalkylamino; and R₅ is selected from the group consisting of bis(alkoxy)methyl, bis(alkylthio)methyl, and --HC═X₂, where X₂ is oxygen or sulfur; provided that R₃ is not hydrogen, hydroxyl, alkoxycarbonyl, or alkoxyl when X₁ is oxygen or sulfur; n is 0; R₄ is hydrogen, methyl, or nitro; R₂ is hydrogen, alkyl, alkoxyl, or halogen; and R₁ is alkyl or aryl.
 2. The compound of claim 1, wherein R₅ is --HC═X₂.
 3. The compound of claim 2, wherein X₂ is oxygen.
 4. The compound of claim 3, wherein X₁ is oxygen or sulfur.
 5. The compound of claim 4, wherein R₂ is cyano.
 6. The compound of claim 5, wherein n is between 1 and 4, and R₆ is selected from the group consisting of aryl, heteroaryl, and arylcarbonyl.
 7. The compound of claim 6, wherein X₁ is sulfur, n is 1, Y is methylene or methylmethine, and R₆ is selected from the group consisting of aryl and heteroaryl.
 8. The compound of claim 7, having the structure ##STR15## wherein R₇ -R₁₁ are selected independently from the group consisting of hydrogen, alkyl, aryl, aralkyl, halogen, alkoxyl, aryloxyl, aralkoxyl, heterocycle, and nitro, and wherein adjacent phenyl ring substituents together can form a 5- or 6-membered cyclic alkyl ether or carbocycle.
 9. The compound of claim 8, wherein R₃ and R₄ are hydrogen, and R₇ -R₁₁ are selected independently from the group consisting of hydrogen, methyl, ethyl, 2-phenylethylenyl, trifluoromethyl, fluoro, chloro, bromo, phenyl, benzyloxy, trifluoromethoxy, isopropyl, and nitro, and wherein adjacent substituents together form points of attachment for the groups --Z₁ --CH₂ --Z₂ --Z₃ -- or --O--(CH₂)_(p) --O--, where Z₁ -Z₃ are selected independently from the group consisting of oxygen, methylene and dimethylmethylene, and p is 1 or
 2. 10. The compound of claim 9, wherein R₇ -R₁₁ are selected independently from the group consisting of hydrogen, methyl, trifluoromethyl, phenyl, and chloro.
 11. The compound of claim 10, wherein each of R₇ -R₁₁ is methyl.
 12. The compound of claim 10, wherein R₇, R₈, R₁₀ and R₁₁ are selected independently from the group consisting of hydrogen and chloro, and R₉ is selected from the group consisting of hydrogen, phenyl, trifluoromethyl, and chloro.
 13. The compound of claim 12, wherein R₇ and R₁₁ are chloro and R₈ -R₁₀ are hydrogen.
 14. The compound of claim 12, wherein R₇, R₈, and R₁₁ are hydrogen, R₁₀ is hydrogen or chloro, and R₉ is chloro, phenyl, or trifluoromethyl.
 15. The compound of claim 14, wherein R₉ and R₁₀ are chloro.
 16. The compound of claim 14, wherein R₉ is trifluoromethyl and R₁₀ is hydrogen.
 17. The compound of claim 9 having the structure ##STR16##
 18. The compound of claim 9 having the structure ##STR17##
 19. The compound of claim 7, wherein R₆ is naphthyl or substituted naphthyl.
 20. The compound of claim 7, wherein R₆ is heteroaryl.
 21. The compound of claim 20, wherein R₃ and R₄ are hydrogen.
 22. The compound of claim 21, wherein R₆ is thienyl, thiazolyl, 1,2,4-oxadiazolyl, or benzo b!thiophenyl.
 23. The compound of claim 22 wherein R₆ is 5-chloro-2-thienyl.
 24. The compound of claim 6, wherein n is 1 or 2, X₁ is sulfur, Y is methylene, and R₆ is arylcarbonyl.
 25. The compound of claim 24, wherein n is 1, R₃ and R₄ are hydrogen, and R₆ is phenylcarbonyl or substituted phenylcarbonyl.
 26. The compound of claim 25, wherein R₆ is selected from the group consisting of (3,4-dichlorophenyl)carbonyl, (2,4-dichlorophenyl)carbonyl, and (4-chlorophenyl)carbonyl.
 27. The compound of claim 6, wherein X₁ is oxygen, n is 1, Y is methylene, and R₆ is phenyl or substituted phenyl.
 28. The compound of claim 27, wherein R₃ and R₄ are hydrogen, and R₆ is 3,4-dichlorophenyl.
 29. The compound of claim 1, wherein n is 1, Y is methylene, and R₆ is a linker L selected from the group consisting of aryl and alkyl, said compound having the structure ##STR18## wherein m is an integer between 2 and
 4. 30. The compound of claim 29, wherein X₁ is sulfur and R₂ is cyano.
 31. The compound of claim 30, wherein R₅ is dialkoxymethyl.
 32. The compound claim 30, wherein R₅ is --HC═X₂, wherein X₂ is oxygen or sulfur.
 33. The compound of claim 32, wherein X₂ is oxygen.
 34. The compound of claim 33, wherein R₃ and R₄ are hydrogen.
 35. The compound of claim 34, wherein L is aryl.
 36. The compound of claim 35, wherein m is 2 and L is phenylene, substituted phenylene, naphthylene, substituted naphthylene, anthrylene, or substituted anthrylene.
 37. The compound of claim 36, wherein L is selected from the group consisting of 2,4-dimethyl-1,5-phenylene, 2,4,6-trimethyl-1,3-phenylene, 1,3-phenylene, 1,2-phenylene, 1,4-phenylene, 2,3,4,5-tetramethyl-1,6-phenylene, 2,5-dichloro-1,4-phenylene, 2,3,4,6-tetramethyl-1,5-phenylene, 2,5-dimethyl-1,4-phenylene, 2,2'-biphenylene, 4,4'-dibromo-2,2'-biphenylene, 2,3-naphthylene, 1,8-naphthylene, 2,3,5,6-tetrachloro-1,4-phenylene, 9,10-anthrylene, and 1,2-naphthylene.
 38. The compound of claim 36, wherein m is 3 or 4 and L is phenylene or substituted phenylene.
 39. The compound of claim 38 having the structure ##STR19##
 40. The compound of claim 38 having the structure ##STR20##
 41. The compound of claim 38 having the structure ##STR21##
 42. The compound of claim 34, wherein L is alkyl.
 43. The compound of claim 42 wherein L selected from the group consisting of ethylene, ethenylene and ethynylene.
 44. A method of treating cancer in a mammal, comprising administering to such mammal a therapeutically effective amount of a compound having the structure shown in claim 1 to inhibit telomerase activity in cancer cells in such mammal such that the telomeres of said cancer cells are reduced in length over successive cell divisions.
 45. A composition for treating cancer, comprising a therapeutically effective amount of a compound having the structure shown in claim 1 in a pharmaceutically acceptable carrier. 